1. Field of the Invention
The invention relates, generally, to printing units, and more specifically, to a printing unit having an improved cylinder throw off capability.
2. Description of the Related Art
A printing unit has a plurality of rotatable printing cylinders. For example, an offset printing unit has a plate cylinder and a blanket cylinder. The plate and blanket cylinders are supported at their opposite ends for rotation in a frame of the printing unit. The plate cylinder carries a printing plate having a surface on which an inked image is defined. The blanket cylinder carriers a printing blanket. When the cylinders rotate in the printing unit, the plate on the plate cylinder transfers the inked image to the blanket on the blanket cylinder. The blanket on the blanket cylinder subsequently transfers the inked image to a signature being printed such as a web or sheet.
A printing unit typically includes a skew mechanism to skew the plate cylinder relative to the blanket cylinder. When the plate cylinder is skewed relative to the blanket cylinder, an angular position of the plate on the plate cylinder is changed relative to the blanket on the blanket cylinder. The angular position of the inked image that is transferred from the plate to the blanket and subsequently to the web is likewise changed. The alignment of the image with the web is thus adjusted by adjusting the skew mechanism.
The printing unit also includes a throw-off mechanism. When the printing plate and/or the printing blanket are to be serviced or replaced, the cylinders are moved relative to each other into thrown-off positions. In this manner, the cylinders are spaced from each other to permit access to the printing plate, the printing blanket and the web. The existing throw-off mechanisms have become quite complex and expensive and thus add to the cost and reliability of the printing unit.
It is accordingly an object of the invention to provide a mechanism for actuating the throw-off of cylinders using eccentric boxes that overcomes the herein-mentioned disadvantages of the heretofore-known devices of this general type, which utilizes eccentric boxes that can be driven by smaller and less complicated actuation assemblies.
With the foregoing and other objects in view there is provided, in accordance with the invention, a printing unit, containing:
a frame;
printing cylinders, including:
a first plate cylinder;
a first blanket cylinder;
a second blanket cylinder mounted in the frame and forming a nip with the first blanket cylinder for receiving a web of material to be printed; and
a second plate cylinder;
a plurality of eccentric boxes mounted on the printing cylinders and supported in the frame; and
a plurality of actuation assemblies, one of the actuation assemblies connected to each of the eccentric boxes for moving the eccentric boxes such that the printing cylinders can be selectively positioned between a thrown-off position and an engagement position in regards to adjacent printing cylinders.
Because of the offset positions of the axes of the eccentric box and a respective cylinder, a rotation of the eccentric box will move the cylinder to a thrown-off position. The eccentric boxes have a mechanical advantage over the prior art devices and can apply the force from the actuation cylinders to the printing cylinders much more effectively than the devices taught in the prior art. Therefore, lower rated and less complicated actuation assemblies can be used which results in reduced manufacturing costs, reduced maintenance costs and higher reliability. In addition, a more compact configuration of the printing unit is also possible.
In accordance with an added feature of the invention, each of the printing cylinders have a first end and a second end, and one of the eccentric boxes is disposed on the first end and the second end of each of the first plate cylinder, the first blanket cylinder and the second plate cylinder.
In accordance with an additional feature of the invention, there are a plurality of bearings disposed in the eccentric boxes for supporting the first plate cylinder, the first blanket cylinder and the second plate cylinder in a journaled manner.
In accordance with another feature of the invention, there are a plurality of cylinder boxes mounted in the frame and housing some of the eccentric boxes. The frame of the printing unit has a gear side and a work side, and the cylinder boxes are supported on the work side of the frame and house the eccentric boxes that are disposed on the first end of the first plate cylinder, the first blanket cylinder and the second plate cylinder. The cylinder boxes each have a pivot point around which the cylinder boxes pivot between a first position in which the eccentric boxes are housed in the cylinder boxes and a second position in which the printing cylinders extend from the frame in a cantilevered manner. In addition, the cylinder boxes each have a moveable part that is movable into an engagement position with the eccentric boxes for clamping the eccentric boxes in position with regard to the cylinder boxes. Each of the cylinder boxes has a lockable toggle handle mechanism connected to the moveable part for moving the moveable part between an open position and an eccentric box clamping position.
In accordance with another added feature of the invention, each of the actuation assemblies has an actuation device selected from the group consisting of pneumatic cylinders, hydraulic cylinders, electrically actuated cylinders and electromagnetic devices, and the actuation assemblies each have a rod member with a first end connected to and driven by a respective actuation device and a second end connected to a respective eccentric box.
In accordance with another additional feature of the invention, there is provided a lever arm connected to the rod member and a link. The link has a first end connected to the lever arm and a second end connected to the respective eccentric box.
In accordance with yet another feature of the invention, the printing cylinders each have an axis and the eccentric boxes each have a main axis offset in regards to the axis of the printing cylinders.
In accordance with a further added feature of the invention, there is provided a plurality of sleeves, and one of the sleeves surrounds each of the eccentric boxes.
In accordance with a concomitant feature of the invention, the eccentric boxes are each formed of a sleeve part and a bearing support part, and the actuation
assemblies are connected to the sleeve part of the eccentric boxes. Other characteristic features of the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a mechanism for actuating the throw-off of cylinders using eccentric boxes, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.